The present invention relates to an intake air amount detecting apparatus (and a method thereof) for detecting an intake air amount of an engine by distinguishing between the forward flow and the reverse flow.
Japanese Unexamined Patent Publication No. 11-182318 discloses an airflow meter that outputs a voltage 1V in a state in which an intake air amount is 0, outputs a voltage higher than 1V as an air amount in a forward direction is increased, and outputs a voltage lower than 1V as an air amount in a reverse direction is increased.
In the case in which a cylinder intake air amount is obtained using the airflow meter, it is necessary to distinguish between the forward flow and the reverse flow. A method of distinguishing between the forward flow and the reverse flow includes the steps of (a) indicating, for example, the forward flow by a positive sign and the reverse flow by a negative sign; and (b) converting, in a conversion table, the output voltage from the airflow meter into intake air amount data.
In the above conversion table, half of an expressible numeric range is used for expressing the air amount on the negative sign side. However, there is caused a problem in that, as the range of change in flow amount on the reverse flow side is narrower than that on the forward flow side, a conversion table capable of expressing a large reverse amount, which is never actually generated, lowers the resolution for intake air amount detection.
As a result, if the number of bits in the intake air amount data is increased, it becomes possible to ensure the necessary resolution. However, this solution heavily consumes memory capacity.